[ptx] VIGRA and alpha channel

[Andrew C Mihal]

Hi,
    I've been looking at porting enblend to use VIGRA for image import and 
export, so that we can work with 16-bit images and the other formats that 
are available. Oddly, support for RGB + Alpha images seems to be absent 
from vigra (I've been looking in tiff.hxx). I suppose that a full set of 
RGBA accessors, iterators, etc. would be necessary. Has anyone made these 
already? Is there a better way to do this?

Andrew

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Andrew Mihal
www-cad.eecs.berkeley.edu/~mihal
mihal at eecs.berkeley.edu